Technical Abstract:
Açaí is a tropical berry from Brazil. Açaí has attracted much attention due to its nutritional value and high content of anthocyanins, resulting in antioxidant and anti-inflammatory activities. Edible films made from fruits can be used as antimicrobial packaging, in which the mechanical and barrier properties from the film-forming components are combined with the color and flavor components of the fruits and the antimicrobial activity obtained from added natural compounds. Thyme essential oil (TEO) and apple skin polyphenol (ASP) are natural compounds considered GRAS by FDA, with biological effects against bacteria and fungi, and have pharmaceutical and therapeutic potential. The main objective of this study was to evaluate the antibacterial activity and physical properties of açaí edible films incorporated with TEO and ASP at 3 and 6 % (w/w). Antimicrobial activity against Listeria monocytogenes was determined using the overlay diffusion test. Physical properties studied include mechanical resistance, water vapor permeability (WVP), color and thermal resistance. Açaí edible films with TEO presented higher antimicrobial activity against L. monocytogenes than ASP at tested concentrations. A synergy among both antimicrobials was observed when incorporated at same concentration in edible films. Tensile strength and elastic modulus were improved by the addition of ASP, while these properties were slightly reduced with TEO. Addition of both antimicrobials used in this study did not affect WVP of açaí edible films. The incorporation of ASP contributed to the lightness of the edible films, while the presence of TEO diminished it when compared to the control. ASP film presented the highest value of a*, while TEO showed a decrease in this reddish coloration. Both antimicrobials individually resulted in a diminished value of b* when compared to the control. Addition of ASP resulted in the highest thermal stability compared to the other treatments. TEO film showed the least thermal resistance.
Industry relevance:
The study of physical properties of edible films is essential for industrial application. However, few works have combined studies of antimicrobial activity with the effects of antimicrobials on packaging physical properties. This work showed the potential application on food preservation of açaí edible films due to their antibacterial activity and synergistic combination of both antimicrobials